The present invention relates generally to fuel injection systems for internal combustion engines.
More particularly, the present invention relates to a pressure-regulated fuel injector having two, serially connected control valves.
In fuel injection systems with high pressure collecting chambers (common rail), which maintain a high pressure in the system, the initiation of injection and the end of the injection are adjusted with electrically adjustable injectors. The injectors are secured with grip-spring tensioning elements onto the cylinder head of the internal combustion engine, without significant changes to the cylinder head. However, under high pressure, such injectors with a smaller valve wear covering can lead to considerable leakage, which commonly impairs the operation of the injectors.
DE 197 01 879 A1 discloses a fuel injection device for combustion engines which includes a high pressure pump arranged with a high pressure-collecting chamber (common rail) filled with fuel. The high pressure-collecting chamber is connected via an injection line with an injection valve projecting into the combustion chamber of the internal combustion engine. The opening or closing movements are controlled, respectively, by an electrically controlled control valve. The control portion is formed as 3/2-way valve, which is connected with the injection line or a release line to a high-pressure channel flowing to an injection opening of the injection valve. A hydraulic working chamber, or pressure release chamber, fillable with high-pressure fuel, is provided on a control member. The working chamber is controllable through adjustment of the set position of the control member in a release channel.
It is therefore an object of the present invention to provide a pressure-controlled injector which avoids the disadvantages of the prior art.
More particularly it is an object of the present invention to provide a pressure-controlled injector which avoids the leakage problem noted above.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a pressure controlled injector which has an injector for injecting fuel in a combustion chamber of an internal combustion engine, comprising a housing provided with a housing opening; a control valve body vertically movable in said opening of said housing; a ring chamber which encloses said control valve body; an inlet connectable with a high pressure collecting chamber and opening into said ring chamber; a nozzle inlet arranged so that during the vertical movement of said control valve body said nozzle inlet is connected with said inlet or separated from the latter; and 2/2-way control valves arranged inside said housing in series so that one of said 2/2-way control valves is force-equalized in an open condition.
The two-way valves (2/2 valves) of the present invention, which are serially connected, allows the upper control valve portion, on which the constant high pressure from the high pressure collecting chamber is based, to be formed in an opened position for regulating or equalizing force, since the valve diameter of the control member of the upper two-way valve corresponds to the guide diameter. Consequently, the two-way control valve which interrupts the high pressure from the high pressure-receiving chamber regulates in a direct way, via a controllable operating unit, such as a piezoregulating unit, which is connected to a hydraulic converter.
A 2/2-way valve, formed as a simple and inexpensive ball valve, is connected on the waste oil side near the force regulating unit of the valve body of the upper 2/2-way valve which interrupts the high pressure from the high pressure collecting chamber, as described above. The ball valve is pressed into its sealing seat when the piezo-regulating unit is controlled and its opening movement opposed. Upon maximum opening of the upper 2/2-way valve, a defined closing of the ball of the lower 2/2-way valve is ensured, so that the disadvantageous results, such as an increase in leakage with small valve wear coverings, are corrected.
Upon closing of the upper 2/2-way valve, the nozzle inlet to the nozzle chamber of the injection nozzle can be released via a ball element of the lower 2/2-way valve, which is disposed in a hollow chamber on the housing side. Based on the fact that the ball body of the lower 2/2-way valve is acted upon with a pressure spring force, the waste oil valve, which operates to counter the piezo element, can close the control valve body of the upper 2/2-way valve (or assist in its closing movement in a vertical direction).
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.